| 摘要 |
PCT No. PCT/SE91/00254 Sec. 371 Date Oct. 9, 1992 Sec. 102(e) Date Oct. 9, 1992 PCT Filed Apr. 9, 1991 PCT Pub. No. WO91/15652 PCT Pub. Date Oct. 17, 1991.A down-the-hole hammer includes a drill bit and a piston reciprocating therebehind to periodically strike the drill bit. The drill bit includes front and rear portions of difference impedance, and the piston includes front and rear portions of difference impedance. In the drill bit, the front portion has a larger impedance than the rear portion. In the piston, the rear portion has a larger impedance than the front portion. |
